For two years, after the resumption of hostilities in May 1803, Britain is the only nation at war with France. Napoleon returns to the scheme of 1798 for an invasion across the Channel, but now on a much more elaborate scale.

In ports from Brest to Antwerp he gathers a fleet of nearly 2000 craft for the transport of men, horses and artillery. During 1803 he assembles what later becomes known as the Grand Army, amounting to some 150,000 men bivouacked (so as to remain inconspicuous) in four widely separated camps but ready to converge at any moment on Boulogne for embarkation. Meanwhile the British, well aware of the threat, are dotting their south coast with the circular fortifications known as Martello towers.

Napoleon's initial plan is for his fleet to launch on a single tide and to cross the Channel unobserved, perhaps under cover of fog, and so escape the attentions of the British navy. But this is impractical for such large numbers. He needs a fleet capable of protecting the invading force.

In December 1804 Napoleon persuades Spain to join him in war against Britain, thus acquiring the support of the Spanish navy. His strategy is now to divert the British fleet, or at least part of it, from guard duty in the Channel.

The result, during 1805, is a game of maritime cat and mouse - with French and British squadrons criss-crossing the Atlantic, between the West Indies and the European coast, in an attempt to second-guess and outwit each other. With the primitive communications of the day, it is difficult even for allied fleets to achieve an intended rendezvous in distant waters. Inevitably Napoleon's somewhat elaborate plans go adrift.

In August the combined French and Spanish fleet, under the command of Villeneuve, withdraws to Cadiz. But the port is already under observation by three British ships of the line. Word is urgently sent for reinforcements. At the end of September Nelson arrives to take command.

On October 19 Villeneuve sails from Cadiz, intending to head south and enter the Mediterranean. He has thirty-three ships of the line. Nelson shadows his movement from several miles out to sea, keeping his twenty-seven ships of the line out of sight and receiving information by signal from his frigates.

Nelson closes in, off Cape Trafalgar, on the morning of October 21. The battle begins just before noon. Five hours later some nineteen French and Spanish ships have surrendered or been destroyed, with no British losses. But Nelson himself is dead, mortally wounded on the deck of the Victory by a sniper firing from the topmast of the Redoutable.

Trafalgar confirms Britain's reputation at sea and has the effect of preventing the French fleet from playing any major part in the remaining years of the war - though Napoleon keeps ships of the line in readiness in French harbours, putting Britain to the considerable expense of mounting permanent blockades.

In his struggle with Britain, Napoleon now reverts to the longer-term strategy of sealing the continent against British goods in the policy which becomes known as the Continental System. But meanwhile others of his old enemies are up in arms again, and he is back in his element - on the battlefields of Europe.

The European board game: 1805-1809

Continental Europe returns to war when Britain persuades Russia, Sweden and Austria to join her in 1805 in a Third Coalition against France. During the next four years Austria drops out at the end of 1805; Prussia joins in on Britain's side in 1806; Prussia and Russia change sides in 1807; Austria re-enters the fray in 1808 against Britain and in 1809 against France.

This chaotic shifting of alliances reflects an important reality of continental Europe at this time. Three major powers (France, Russia, Austria) surround a central area comprising many smaller states (in Germany and Italy) among which, with Napoleon vigorously shaking the dice, almost everything is up for the taking.

The faded fragments and tatters of the Middle Ages form a patchwork of imperial cities and small territories ruled by bishops, counts and knights. They are easy prey for their powerful neighbours. As in a board game, they can be distributed at will among the major players.

Even quite significant rulers can be pushed around. An example is Ferdinand III, grand duke of Tuscany. In 1801 France and Austria agree that Tuscany shall become the kingdom of Etruria with a new ruler. In compensation Ferdinand is given Salzburg, previously belonging to an archbishop. In 1805 he is forced to exchange this for the ex-bishopric of Würzburg. By 1814, with the fall of Napoleon, he is back in Tuscany.

This is just one example of the upheavals occurring all over central Europe at this time, as Napoleon rearranges the map after each stage of his victorious progress. His opponents fail to achieve a convincing alliance against him because they are primarily interested in preserving their own territories and in acquiring any others which may become available.

With the exception of Britain, implacably opposed to France as a world-wide competitor, Napoleon's other opponents enter or drop out of the fray on anhoc basis of self-interest.

Napoleon against Russia and Austria: 1805

When Russia and Austria declare war on Napoleon in 1805 (in the Third Coalition), he is able to find allies in Germany who are eager to see Austria's power reduced. Prussia remains neutral, but Bavaria and two other territories in southwest Germany come in on France's side. Their region sees the first encounter in this new phase of the war. Moving fast along the Danube, Napoleon gets between the Austrians and their approaching Russian allies. In October 1805 he surrounds the Austrians at Ulm. More than 50,000 troops are captured with minimal French losses.

The French reach Vienna on November 12 and enter the city unopposed. They quickly move on, pursuing a joint Russian and Austrian army into Moravia.

The eventual encounter takes place on December 2 at Austerlitz. The allied army, under the command of the Russian general Kutuzov, outnumbers the French by a wide margin (90,000 men to 68,000). In spite of this, the day goes decisively to the French.

The victory ends any immediate threat to Napoleon from the Third Coalition. The Russians limp back home after agreeing a truce. The Austrian emperor, Francis I, signs a peace treaty with Napoleon at Pressburg on December 26. He cedes to Napoleon the entire northern coast of the Adriatic, consisting of the provinces of Venetia (meaning Venice and its surrounding region), Istria and Dalmatia.

At Pressburg Francis I is also forced to recognize a new status for Napoleon's three German allies in the recent campaign, Bavaria, Baden and Württemberg. Their rulers receive marked increases in status (as kings now of Bavaria and Württemberg, and grand duke of Baden), but the improvement is more nominal than real.

A few months later, in July 1806, Napoleon merges the two new kingdoms and the grand duchy, together with several smaller principalities, into a single Confederation of the Rhine - a vassal state under the protection of France.

Confederation of the Rhine: 1806-1807

The simplifying of Germany's feudal patchwork, to France's advantage, has begun in 1801 after the peace of Lunéville cedes the left bank of the Rhine to France. The understanding is that German rulers with lands west of the Rhine will receive compensation elsewhere. This is to be provided from the many ecclesiastical territories and small imperial cities in the fragmented Holy Roman empire, too weak to resist their forcible redistribution among the larger players.

A commission is set up to consider the precise allocations. Its proposals, distributing to new owners 112 previously independent territories, are presented and accepted in 1803.

This unifying process, carried through under duress, is further advanced after Napoleon's defeat of the Austrians in 1805. His German allies in that war are rewarded by enlargement of their realms at the expense of weaker neighbours (and also by nominal increases in rank).

But the greatest act of rationalization comes in 1806 when Napoleon merges the whole of Germany east of the Rhine, with the exception of Prussia and Saxony, into the Confederation of the Rhine. Saxony joins this Francophile family a year later, in 1807, with its elector raised to the status of king.

The members of the Confederation continue to regulate their own internal affairs, but they acknowledge Napoleon's superior status as 'protector' of their union. They are banned from pursuing an independent foreign policy, and they must place troops at his disposal when required.

They have in effect exchanged an ancient feudal commitment for something identical in modern guise, shifting their allegiance from one emperor to another. But this yoke will last only as long as the new emperor. A much more coherent Germany emerges from the Napoleonic era. And the example inspires many with an increasingly important dream of the 19th century - that of a single German nation.

Napoleon against Russia and Prussia: 1806-1807

Until 1806 Prussia maintains a nervous neutrality during the warfare between its powerful neighbours. But the Confederation of the Rhine, organized by Napoleon in July of this year, seems to threaten Prussian interests. In September Frederick William III joins Russia against Napoleon.

The result is rapid disaster. Once again Napoleon moves quickly enough to destroy one of his opponents before the other can arrive in support. Two Prussian armies are engaged on the same day, 14 October 1806, at Jena and Auerstadt - about thirteen miles apart.

At both sites the French are victorious. Within six weeks, before Russian assistance arrives, Napoleon overruns the whole of Prussia.

The Russians prove, at first, rather tougher opponents. A two-day engagement at Eylau (7-8 February 1807) brings heavy casualties but no advantage to either side. But at Friedland, on June 14, Napoleon wins a decisive victory over the Russian army. The result is the extraordinary meeting between Napoleon and the Russian tsar, Alexander I, on 25 June 1807 near Tilsit. Neither will set foot on territory held by the other, so it is agreed that they will meet in the middle of the river, the Neman, which forms the border between them.

An elegant room is built on a raft with a door on either side, each showing the appropriate imperial eagle. The two emperors cast off from their respective river banks at the same moment, but the French oarsmen outrow the Russians. Napoleon is far enough ahead to be able to open the Russian door from the inside and greet the tsar.

The two men get on well. Together they set about carving up Europe. After two weeks of conference Russia's ally Prussia has been gravely weakened, by mutual agreement between the emperors. Russia could easily have fought on after Friedland. But Prussia is occupied by the French and is helpless.

Prussia's share of Poland is taken to provide a grand duchy of Warsaw, to be ruled by the king of Saxony (a newly acquired ally of Napoleon). Prussian territory is severely reduced in similar fashion in the west to make room for a kingdom of Westphalia. French troops will remain in Prussia until an indemnity of 120 million francs has been paid. And Prussia is to close her ports to Britain as part of Napoleon's new Continental System.

Russia also agrees to join the Continental System in certain circumstances and according to a clear timetable, laid down in one of the secret clauses in the Tilsit agreement.

Russia and France will together demand of Britain that she allows freedom of the seas to ships of all nations and that she returns any territories seized since 1805. If this is not agreed by November 1807, the two emperors will insist that Sweden, Denmark and Portugal (the only nations still neutral or allied to Britain) close their ports to British ships and join France and Russia in declaring war.

If an invasion of Sweden proves necessary, France will have no objection to the Russian annexation of Swedish Finland. Moreover France will give diplomatic support to Russia against Turkey in the Balkans. The two emperors are in satisfactory agreement.

One big European family:1808

The agreement at Tilsit, together with other refinements over the next twelve months, brings Napoleon in 1808 to the peak of his power.

He now governs, either directly or through his close relations, the following regions: France within its 'natural frontiers' of Pyrenees, Alps and Rhine; the Netherlands (the kingdom of Holland, ruled by brother Louis); northwest Germany (the kingdom of Westphalia, brother Jérôme); and most of Italy (Tuscany under direct rule, the kingdom of Italy under stepson Eugène de Beauharnais as viceroy, the kingdom of Naples under brother Joseph). Spain follows in 1808, when Joseph is transferred to that throne - leaving room for a new king of Naples, brother-in-law Joachim Murat.

Meanwhile Napoleon's client states cover the rest of Germany (the Confederation of the Rhine), part of what was once Poland (the grand duchy of Warsaw) and Switzerland (the Helvetic republic). Portugal is an irritating exception - officially neutral, but by long tradition a friend of Britain.

The agreement at Tilsit, bringing peace to continental Europe, leaves Napoleon free to focus his attention once again on his main enemy, Britain - and on the Continental System. His immediate problem is the need to make this system fully effective.

The Continental System: 1806-1807

The purpose of Napoleon's Continental System is to ruin Britain's economy by preventing British goods from reaching any market in continental Europe. It is not, as it would be in modern warfare, an attempt to starve an island enemy into submission.

Educated in the 18th-century mercantilist school of economics, Napoleon believes that nations thrive primarily through wealth earned abroad. He therefore allows surplus French corn to be sold to Britain in 1809 and 1810, even though a shortage is already causing his enemy grave difficulty in high bread prices. Nevertheless a complete blockage of British exports would in itself be extremely damaging if it could be made watertight.

Napoleon begins to build his system when he is wintering in Berlin after defeating the Prussians at Jena. In November 1806 he issues the Berlin decree, denying the ports of France and her allies to any ship sailing from Britain or a British colony.

This proves insufficient, since it fails to prevent a neutral ship from bringing in British goods. At Fontainebleau in October 1807, and in Milan a month later, Napoleon adds extra clauses: all colonial goods entering a port will be regarded as British unless producing some other certificate of origin; and any ship submitting to British orders in council, or sailing from or to Britain, will be regarded as a lawful prize if seized at sea.

The orders in council, issued in January and November 1807, are Britain's response to the decrees that put in place the Continental System. In them the British government states that any port closed by this system is now considered under blockade; and that any vessel trading into such a port must first receive a licence from Britain, paying customs of 20% or more on its cargo. The effect of these measures and counter-measures is particularly damaging to neutral ships, which now risk being apprehended at sea by the British and in port by the French.

Meanwhile, from Napoleon's point of view, the immediate practical problem is to ensure that every European nation with a coastline joins his scheme.

By the end of 1807 Denmark, Russia, Prussia and Austria have done so. Sweden, an ally of Britain's from the start of the Third Coalition, refuses to comply - so, as planned at Tilsit, she is invaded by Russia (in February 1808).

Securing the Baltic may be left to Russia, but the Iberian peninsula is clearly France's own responsibility. Spain is a feeble ally of France, usually acting only under compulsion. Portugal is at best a neutral nation with a soft spot for Britain. This unsatisfactory situation tempts Napoleon into an undertaking which harms his cause in the Iberian peninsula, and becomes one of the factors in his ultimate downfall.

Spain and Portugal: 1807-1809

In October 1807 Napoleon decides that the only certain method of securing the Continental System is a French occupation of Portugal. He despatches an army for the purpose and summons Spanish envoys to Fontainebleau.

In a treaty signed at Fontainebleau, on October 27, the partition of Portugal is agreed. France is to have the central section, including Lisbon and Oporto. The Algarve in the south will go to Godoy, the Spanish king's unscrupulous chief minister. The north will be granted to the young duke of Parma in return for his valuable kingdom of Etruria (or in plain terms Tuscany), which will be ceded to France.

Even before the treaty is signed a French army has entered Spain on its way to Portugal - where its imminent arrival near Lisbon causes panic. The royal family and court decide to flee for safety to Brazil, taking with them (to Napoleon's fury) the gold and silver of the national treasure. A Portuguese fleet, accompanied by a British squadron, sails from the mouth of the Tagus on 29 November 1807. The vanguard of the French army enters the capital city the next day.

It will be fourteen years before the return to Lisbon of a Portuguese monarch. But the French are to have only a very short tenure. Their intrusion launches the Peninsular War. Before a year is out, the British are in the city.

Meanwhile the French are stirring up further trouble for themselves elsewhere in the Iberian peninsula. Troops move from France into northern Spain, ostensibly to support their colleagues in Portugal but looking alarmingly like an army of occupation. In February 1808 they seize Barcelona. In mid-March a force under Murat moves south towards Madrid.

This news causes Godoy to persuade his king, Charles IV, to follow the Portuguese example and flee to Latin America. But on the way south an outraged patriotic mob corners the royal party at Aranjuez. They escape with their lives only when it is agreed that Charles will abdicate in favour of his son Ferdinand, and that the hated Godoy will be imprisoned and brought to trial.

The new king immediately spoils his own chances by returning to Madrid, reaching it on March 24 - just one day after Murat has arrived and captured the city.

There follows a typical piece of power play by Napoleon. Both kings of Spain, father and son, are invited to Bayonne - just over the border in France - and are there persuaded, by a combination of trickery and duress, to abdicate in favour of Napoleon's choice for the Spanish throne. He has already selected his brother Joseph, who at present is king of Naples (a dignity now to be transferred to Murat). This is politics at its most cynical. But just a few days earlier a much more significant event has occurred in Madrid.

On May 2 a French platoon is escorting a coach containing the youngest son of Charles IV. A furious mob attacks them. The soldiers disperse the crowd with some rounds of shot, whereupon the whole of Madrid erupts in an explosion of popular rage. More than thirty French officers and hundreds of soldiers and civilians are killed or wounded before order is restored.

Murat reasserts French authority with brutal reprisals, but the event provokes a spirit of passionate resistance (famously captured in Goya's painting of a street execution, entitled 3 May 1808). This spirit spreads rapidly through Spain.

Instead of the docile monarchy of recent years, Napoleon is now confronted on his southern border by a popular uprising. His brother Joseph arrives in Madrid on July 20 to enjoy his new dignity. Two days later a French army is defeated by insurgents in Andalusia, at Bailén, with the loss or capture of some 17,000 men. By the end of the month King Joseph (nominally of Spain and the Indies) has abandoned his new capital city, withdrawing for safety's sake 150 miles northeast beyond the Ebro river.

Spain takes its place, with Portugal, as one of the theatres of the Peninsular War - which will last six years and be a constant drain on Napoleon's resources.

Austria's expensive adventure: 1809

During the last two months of 1808 Napoleon takes personal charge of the campaign in the Peninsular War. His absence in Spain, with large numbers of French troops, prompts the Austrians to re-assert themselves. As many as three archdukes (brothers of the emperor Francis) prepare to take the field with armies pressing south into Italy, north towards Warsaw and west into southern Germany.

The largest force, under archduke Charles (by far the most distinguished soldier in the imperial family), moves west along the Danube and enters Bavaria in April 1809. By then Napoleon has hurried back from Spain to meet this greater threat.

As so often in the past, Napoleon is able to prevent his enemies from making the most of their advantages. Engagements at Abensberg and Eckmühl on April 19-23 leave the Austrians in retreat. By May 13 Napoleon is once more at the gates of Vienna, which are opened to him when he threatens bombardment.

However the archduke Charles is nearby with a large army. The result is a hard-fought battle on May 21-22 around the towns of Aspern and Essling, on the bank of the Danube a few miles from Vienna. Neither side gains a clear advantage. But with Napoleon's invincible reputation, this engagement is seen in Europe as his first serious personal defeat in battle.

Six weeks later the same commanders meet each other again on a plain near the village of Wagram to the northeast of Vienna. The fighting on July 5-6 is extremely heavy, with some 74,000 casualties between the two sides, but this time the day is clearly Napoleon's. The Austrians immediately ask for an armistice.

When the treaty of Schönbrunn (or Vienna) is signed in October 1809, the terms are once again disastrous for Austria. The emperor Francis surrenders further slices of territory - to Bavaria, to the grand duchy of Warsaw, to Russia and to France - losing in the process some 3,500,000 subjects and all his remaining coastline. It will be small consolation that he is about to acquire a son-in-law.